High performance solid rocket motors mandate high ‘volumetric loading fractions’ in propellant grain and flexibility in ‘thrust profile tailoring’ apart from increase in propellant energy levels and lighter and stronger structures. Conventional single-piece casting mandrels limit grain design flexibility in large monolithic solid rocket motors because major transverse dimensions of propellant grain cavities molded using single-piece mandrels cannot be larger than the openings in the monolithic casing. Consequently when required it becomes difficult to avoid increase in burn surface area as the grain web burns beyond the rocket motor case opening diameter. Hence single-piece mandrels in typical monolithic casings reduce overall propulsion system design and performance efficiency. Propellant machining is one way of forming grain cavities larger than casing openings. However, the machining process is slow and hazardous. Therefore, casting of propellant slurry inside the motor casing around a dismantleable mandrel and curing it to the final grain shape, before disassembling the mandrel out of the rocket motor (decoring), is both safe and quick.
Conventional mandrel assembly for distributing propellant inside a solid propellant casing as disclosed in EP1522711 A3 (Milleni et al.) comprises a rigid, strip-down plug which is larger transversely than the opening of the casing. The plug is assembled inside the casing after successively inserting the fin molds and a tubular locating body and by releasably locking the fin molds by means of a hydraulic or mechanical device housed partly in the tubular locating body. However, due to the presence of large number of components with critical joints, the chances of propellant slurry leak or ingress into crevices is more. Hence the process of removal of the mandrel assembly (decoring) from the cured propellant grain becomes more hazardous.
Another conventional dismountable mechanical core and procedure for implementing it as disclosed in U.S. Pat. No. 5,714,081 (Tilac et al.) comprises a dismountable mechanical core that includes a counterform attached to a central mandrel. The components of the counterform are attached to the central mandrel by rod anchoring devices. During the disassembling process, the anchor rods are dismantled from the central mandrel, the central mandrel is then withdrawn and each counterform component is separated. With large number of components, the process of removal of the mandrel assembly (decoring) from the cured propellant grain becomes more hazardous. Furthermore, conventional casting techniques involve machining of the cured propellant grain especially the counter-bore to obtain the final shape of the propellant grain. However the machining process is hazardous and involves the risk of explosion.
Therefore, there is a need for a new mandrel assembly that is simple with less number of parts and joints and a technique for using the mandrel assembly that is safer to manufacture propellant grains with deep cavities and overcome the above mentioned difficulties or problems. Consequently, those skilled in the art will appreciate the present disclosure that provides many advantages and overcomes all the above and other limitations.